function [ ] = mx_eyemsg_printf( )
%MX_EYEMSG_PRINTF This sends a text message to the EyeLink tracker, which 
% timestamps it and writes it to the EDF data file. Messages are useful for
% recording trial conditions, subject responses, or the time of important events.
% This function is used with the same formatting methods as printf(), allowing
% numbers to be included. Avoid end-of-line characters ("
") at end of messages.
%
% Parameters:
% fmt 	Similar to printf(), format string plus arguments.
% Returns:
% 0 if successfully sent to tracker, else error code.
%
%----------------------------------------------------------------------------
% Copyright Eduardo Aponte 2013
% aponteeduardo@gmail.com